The present invention relates to soluble, or instant, coffee. The manufacture of instant coffee involves extracting roasted and ground coffee beans with water under conditions of high temperature and pressure to form extracts which are dried, such as by spray drying, freeze drying or the like. The manufacture of instant coffee causes the loss of a large part of the aroma constituents and of the volatile components of the coffee. As a result, when a cup of instant coffee is prepared, for example by dissolving a portion of instant coffee in a cup of hot water, the beverage is essentially aromaless when compared to a cup of brewed roast and ground coffee. When roast and ground coffee is brewed, a unique aroma is experienced, often perceivable throughout a large room. It is generally recognized in the coffee industry that consumers associate coffee quality with a good coffee aroma. Therefore, a number of attempts have been made to trap coffee aroma lost during coffee processing and to add the trapped aroma to instant coffee to enhance its aroma.
A large number of techniques have been developed to trap coffee aroma, usually in coffee oil or in coffee extract. See, for example, U.S. Pat. Nos. 3,823,242, 5,030,473 and 5,222,364. Aromatized coffee oil is then sprayed onto instant coffee powder or incorporated in it. However, most of the aroma escapes into the container and the aroma is essentially completely lost after three or four openings of the container. Moreover, very little aroma is perceived at the time that a beverage is prepared. Many attempts have been made to address these problems. Such attempts have included attempts to encapsulate aroma in such a way that the aroma is released only when a beverage is prepared by dissolving soluble coffee in hot water. Such aroma release is referred to as xe2x80x9cabove cup aromaxe2x80x9d or simply xe2x80x9ccup aromaxe2x80x9d.
It is desirable to encapsulate aromas and flavors in such a way that they are preserved from degradation due to moisture, oxygen, heat or external/internal molecular product, interactions, and to prevent their volatilization since most aroma compounds are of high volatility. Spray drying which produces an easily handled powdered product is one of the most common aroma encapsulation methods at present. However, a major problem occurring when an aqueous coffee extract is spray dried is the loss of many desirable volatile materials or xe2x80x9ctop notesxe2x80x9d, or a change in composition of the heat-or oxygen-sensitive aromas. These changes and losses can change the overall aroma characteristics and in turn, make them undesirable.
Solutions of matrix materials containing either dissolved or dispersed flavors and aromas can be freeze dried to encapsulate volatile components. However, freeze drying, which leads to a porous and foamy structure of the finished product, also has problems in capturing and encapsulating volatile components.
Other methods of encapsulation include spraying a coffee aroma-containing emulsion as fine droplets onto soluble beverage powder which coats the droplets. When dried, the coffee forms a shell which encapsulates the aroma. Methods of this type are described in European Patent Application 0008015A1 and in published International Application No. WO 96/23423. Although the capsules are satisfactory, large aroma loss occurs during the encapsulation process. Capsule wall formation is not instantaneous and a large amount of aroma is lost during drying of the wall. After drying, the capsules form good walls to retain the aroma and flavor, and the capsules dissolve readily when hot water is added to release the encapsulants. Also the process does not involve heating or vacuum drying steps so there is no loss or change of the volatile components. The capsules when added to a soluble beverage powder, e.g., soluble coffee, enhance or provide additional aroma or flavor upon dissolution of the soluble beverage in hot water. However, the aroma has very small impact, as most of aroma has been lost. The impact of aroma can be increased by increasing the number of capsules, but a large quantity of aroma carrying oil would then be retained on the cup surface. The presence of oil slick has an adverse affect on consumer preference. In addition, aroma is not stoichio-metrically added. The quantity of aroma generated during instant coffee processing is not sufficient enough to provide acceptable in-cup aroma for instant coffee preparation.
Melt encapsulation of aroma or flavor is a known technique in which a carbohydrate melt is prepared and the aroma and/or flavor to be encapsulated added. The solution is then quenched at elevated temperatures using, for example, isopropyl alcohol, producing a solid carbohydrate product containing flavor. Such techniques are disclosed in U.S. Pat. No. 4,610,890 and U.S. Pat. No. 4,707,367. As opposed to a batch type of melt encapsulation just described, in more recent years there has been developed a continuous extrusion melt encapsulation process. In a continuous process described in U.S. Pat. No. 5,079,026, the aroma or flavor is dispersed in an extruded matrix of coffee glass. The coffee extract with a high percentage of soluble solids is heated to form a viscous melt at temperatures typically above 60xc2x0 C., above the glassy transition phase, but below 130xc2x0 C. to prevent degradation of the extract. The encapsulants are then dispersed within the hot viscous melt. The hot viscous melt containing the encapsulants is gasified and then extruded through a restricted orifice into a sheet or rod of coffee glass. After cooling, the sheet or rod is then broken up to the desired size. Considerable thermal degradation of the encapsulants take place in this process, altering their profile when they are added to the hot viscous melt. When a beverage is prepared, a large proportion of the aroma dissolves in the hot water rather than being released above the cup. Moreover, unless the sheet or rod is broken up into very small particles there will not be a xe2x80x9cburstxe2x80x9d of aroma because of the slow rate of dissolution of the coffee glass. It is suggested that gasification of the melt will improve the product""s solubility. However, the procedure has been mainly unsuccessful in releasing a sufficient xe2x80x9cburstxe2x80x9d of aroma for the consumer to be able to detect an above cup aroma.
U.S. Pat. No. 5,399,368 describes a method of encapsulation using a co-extrusion technique. An inert gas, e.g., CO2, is dissolved under pressure in an aromatized edible liquid such as aromatized coffee oil and a melt for forming a rigid outer shell of the capsules is formed from an edible carbohydrate material such as soluble coffee. The edible liquid is then co-extruded within the viscous melt to continuously form an extrudate having an outer shell of edible carbohydrate material surrounding an inner core of the edible liquid. The extrudate is extruded into a pressure zone which has a pressure higher than that of the internal pressure of the inert gas dissolved in the edible liquid. At this point the extrudate is subdivided transversely into sealed capsules of a predetermined length and the capsules are left in the high pressure zone until the melt has formed a hard carbohydrate glass surrounding the aromatized liquid. When placed in hot liquid, the capsule dissolves, releasing the aroma compounds. However, the glass wall dissolves less readily compared to porous spray dried or freeze-dried coffee powder. The delayed dissolution of the glassy wall inhibits an instant burst of aroma. The presence of gas increases the release rate of aroma once the glassy wall is dissolved. When coffee extract is employed, the solids concentration is high (e.g., 92% in Example 1, of U.S. Pat. No. 5,399,368) and co-extrusion is carried out at very high pressures e.g., 200 bar for the coffee melt and 5 bar for the gasified aroma. The outer wall of the capsule is difficult to control due to the large pressure differential. In addition, a rotating knife is used to cut the rod being co-extruded in order to form capsules. It is very unlikely that the outer co-extruded wall is going to seal itself after the rod is cut at both ends. The drying process for the capsules takes a few hours. As a consequence, capsules will tend to stick together during the early period in the drying chamber.
It is an object of the invention to provide capsules which encapsulate aromatized vegetable oil within a shell and which, upon dissolution in hot water, will release a burst of aroma. It is a further object of the invention to provide such capsules which are prepared from 100% coffee-derived material or other carbohydrate materials. It is a further object of the invention to provide such capsules having a shell which has substantially closed cell porosity which reduces the density of the capsules and which facilitates their dissolution without rapid loss of aroma that would occur with open cell porosity It is a further object of the invention to provide a simple method of preparation of such capsules.
The foregoing and other objects which will be apparent to those of ordinary skill in the art are achieved in accordance with the invention by providing individual particles comprising aromatized vegetable oil encapsulated in a solid shell of a porous water soluble encapsulant, the porosity of said shell being substantially closed cell porosity, open cell porosity of said shell being not more than 25% based on the total porosity of said shell. A method of making volatile aroma containing capsules is also disclosed which comprises providing gasified aromatized vegetable oil, providing an aqueous solution containing 50 to 75% by weight of a water soluble encapsulant based on the weight of the extract, forcing the gasified aromatized vegetable oil through a first spray nozzle aperture and simultaneously forcing the aqueous solution of the water soluble encapsulant through an annular spray nozzle aperture which surrounds said first spray nozzle to co-extrude droplets of gasified aromatized vegetable oil surrounded by said encapsulant, and contacting said droplets with a liquid desiccant to dehydrate said droplets to form particles having a solidified shell of a porous encapsulant surrounding aromatized vegetable oil, the porosity of said solidified shell being substantially closed cell porosity, open cell porosity of said shell being not more than 25% of the total porosity of said shell.
The water soluble encapsulants may include, but are not limited to instant or soluble coffee solids, instant tea solids, cyclodextrin, maltodextrin, gelatin, pectin, guar gum, and gum arabic. Preferably the water soluble encapsulant is instant coffee solids. The aromatized vegetable oil may contain flavorants and/or aromatics derived from fruit, meat, seafood, spices, vegetables, etc.; preferably the aromatics are obtained from coffee, tea and chocolate and most preferably the aromatics are obtained from the coffee manufacturing process such as steam aroma, grinder gas, percolator vent gas, etc. The vegetable oils can include, but are not limited to coffee oil, safflower oil, palm oil, peanut oil, soybean oil, corn oil, etc. Preferably the vegetable oil is coffee oil. In the preferred embodiment, the aromatized capsules are prepared from 100% coffee-derived materials, i.e. the encapulant is coffee solids and the aromatized vegetable oil is coffee oil containing coffee aroma. Throughout the remainder of the specification, with the exception of Examples 4 to 9, for purposes of convenience, the water soluble encapsulant shall comprise instant or soluble coffee solids and the aromatized vegetable oil shall comprise aromatized coffee oil. However this is not intended to limit the scope of the invention thereto.